Ethylene production is responsible for the second largest carbon footprint of any high-volume commodity chemical. A significant percentage of these emissions is due to the removal of trace acetylene, which poisons the Ziegler-Natta catalyst used to polymerize ethylene into polyethylene. Acetylene removal is typically performed via semi-hydrogenation to ethylene over Pd-based catalysts. Earth abundant Cu-based catalysts exhibit superior ethylene selectivity due to their near thermoneutral ethylene adsorption energy. Unfortunately, Cu-based catalysts also exhibit low acetylene hydrogenation activity due to their sluggish H2 activation kinetics. However, these limitations can be circumvented by performing acetylene semi-hydrogenation in an electrochemical hydrogen pump. Electrochemical hydrogen pumps are an emerging technology for H2 purification that operate by oxidizing H2 to H+ over the anode and transporting the H+ through a proton-exchange membrane to the cathode, where they are reduced back into H2. These devices can be utilized to perform acetylene semi-hydrogenation by feeding the acetylene stream directly into the cathode chamber. This configuration enables acetylene semi-hydrogenation to be performed over Cu-based catalysts without the kinetic burden of H2 activation, significantly enhancing intrinsic activity. We demonstrate this concept by performing acetylene semi-hydrogenation over Pt and Cu in a reactor setup that enables acetylene semi-hydrogenation to be performed both thermocatalytically and thermo-electrocatalytically at 80 °C. We demonstrate that the mode of operation does not impact the intrinsic activity of metals that can rapidly activate H2, such as Pt. However, the acetylene semi-hydrogenation activity of Cu is enhanced by nearly two orders of magnitude when performed thermo-electrocatalytically. H2/D2 scrambling experiments confirm that the kinetic limitations typically exhibited by Cu arise due to sluggish H2 activation and are further supported by density functional theory calculations and microkinetic modelling. Thus, this presentation demonstrates that hybrid thermo-electrocatalytic reactors exhibit significant advantages over either individual approach.
